def advancing_progression_original():
    """
    Here is a progression of three-note chords that begins with notes [1, 2, 3]
    and ends with notes [4, 5, 6]

    The output of this function is the following:

    [(1, 2, 3), (1, 2, 4), (1, 3, 4), (2, 3, 4), (1, 2, 5), (1, 3, 5), 
    (2, 3, 5), (1, 4, 5), (2, 4, 5), (3, 4, 5), (1, 2, 6), (1, 3, 6), 
    (2, 3, 6), (1, 4, 6), (2, 4, 6), (3, 4, 6), (1, 5, 6), (2, 5, 6), 
    (3, 5, 6), (4, 5, 6)]

    """
    print([(a, b, c)
        for c in range(3, 7)
            for b in range(2, c)
                for a in range(1, b)])


def advancing_progression_one():
    """
    The output of this function is the following:
    [(1, 2, 3), (1, 2, 4), (1, 2, 5), (1, 2, 6)]

    """
    print([(1, 2, c)
        for c in range(3, 7)])

def advancing_progression_two():
    """
    The output of this function is the following:
    [(1, 2, 3), (1, 2, 4), (1, 3, 4), (1, 2, 5), (1, 3, 5), (1, 4, 5), 
    (1, 2, 6), (1, 3, 6), (1, 4, 6), (1, 5, 6)]

    """
    print([(1, b, c)
        for c in range(3, 7)
            for b in range(2, c)])


print("FIRST LEVEL")
advancing_progression_one()
print("SECOND LEVEL")
advancing_progression_two()
print("THIRD LEVEL")
advancing_progression_original()
